As a positive-type photosensitive resin composition, a resin composition that contains a phenol novolac resin, a cresol novolac resin, or a vinylphenol novolac resin (i.e., an alkali-soluble resin that exhibits high sensitivity and high resolution and does not reduce the film thickness to only a small extent), a photoacid generator, and a crosslinking agent has been used (refer to Patent Documents 1 and 2).
In recent years, the wires of a semiconductor element for which the positive-type photosensitive resin composition is used has been reduced in size. Therefore, if the positive-type photosensitive resin composition is cured at a high temperature, the wires of the semiconductor element may be damaged due to heat. The positive-type photosensitive resin composition has been extensively studied to form an insulating film or a protective film of a wafer-level package (WLP). In this case, a deterioration of a transistor may occur if the positive-type photosensitive resin composition is cured at a high temperature.
When the positive-type photosensitive resin composition is used to form an insulating film or a protective film of a semiconductor element, if the cured positive-type photosensitive resin composition has a low glass transition temperature (Tg) and a low modulus of elasticity, cracks may occur in the insulating film or the protective film due to a filler (silica) contained in an encapsulation resin that encapsulates the semiconductor element.
The novolac resin-based positive-type photosensitive resin composition and the norbornene-based positive-type photosensitive resin composition disclosed in Patent Documents 1 and 2 can be cured at a low temperature, but produce a cured film having poor properties (i.e., low glass transition temperature (Tg) and low modulus of elasticity). Therefore, these positive-type photosensitive resin compositions may not be used to form an insulating film or a protective film of a semiconductor element.    Patent Document 1: JP-A-7-199464    Patent Document 2: JP-A-11-258808
In view of the above situation, an object of the present invention is to provide a positive-type photosensitive resin composition that can be cured at a low temperature, and a highly reliable semiconductor device including a cured film of the positive-type photosensitive resin composition.